This invention relates to a system for transferring objects. In particular, the present invention relates to a system for transferring steel slabs.
Steel slabs are semi-finished products obtained in the steel industry. A typical slab may weigh between 20 and 50 tons. Subsequent to casting, slabs are sent to a hot stripmill to be rolled into coiled sheet and plate products.
In a prior arrangement, stacks of steel slabs of various lengths are received from an overhead crane at a slab receiving roller table in a slab receiving area of a hot strip mill. Typical stacks consist of five slabs. The stack is then transferred by roller tables to a slab unpiler roller table. The slab unpiler table is lowered so that the bottom of the top slab of the stack is approximately level with the top of a parallel furnace charging table. Each slab is transferred perpendicularly to the rolling direction from the slab unpiler table to the furnace charging table by a pushing mechanism. The pushing mechanism pushes each slab across the slab upon which it is resting (unless it is the bottom slab of the stack) and onto the furnace charging table. Often slabs are bowed and at ambient temperature can also be at 1000xc2x0 F. when hot charging is required.
Problems arise in that pushing slab over slab or directly over the roller table causes marking, etching and deformation of the slabs, which in turn affects the quality of the end product. Also, the pusher system typically cannot maintain the production time required by the pre-heat furnaces.
Accordingly, an advantage exists for a system to transfer slabs efficiently while minimizing damage.
The present invention provides a system for transferring a steel slab from a first roller table to a second roller table by lifting the top slab from a stack of slabs on the first table, and then transferring and lowering the slab onto the second table. Specifically, in a presently preferred embodiment, the present invention provides a gantry-type bridge trolley mechanism that is motor driven on a cantilevered runway over the slab unpiler table and the furnace charging table. The cantilevered system provides a space-saving advantage by limiting the necessary supports to only one side of the roller tables. Alternatively, in situations where space is not a factor, a crane having supports on both sides of the roller tables could be provided. A lifting device on the trolley mechanism is powered by a self-contained hydraulic actuator with its own power source. The actuator is connected to a center lever arm that is mounted to a horizontal torsional shaft. Spaced on the horizontal shaft are at least two and preferably four additional lever arms. The lever arms are preferably but not necessarily spaced apart at an equal spacing (in instances using three or more arms). Spacing the lever arms unequally along the horizontal shaft ensures that the shortest slabs can be picked up. A vertical rod suspending an electromagnet is operationally connected to each additional lever arm. Each vertical rod and electromagnet combination is structurally designed to be able to support a slab. Although not required, it is desired to have at least two electromagnets pick up a slab for stability purposes. While in the most preferred embodiment four vertical arm and electromagnet combinations are provided, it should be apparent that other numbers are contemplated. Optionally, and preferably, each vertical rod includes a load cell which is operationally connected to a control unit to measure the weight of each slab. Each vertical rod is also provided with a stabilization system to eliminate sway of the vertical rods. While a single actuator preferably controls the vertical position of the electromagnets, each vertical rod and electromagnet combination may have independent actuators.
In operation, the trolley mechanism which is driven by powered wheels positions the electromagnets over the stack of slabs on the slab unpiler table. The hydraulic actuator lowers the electromagnets so that the electromagnets make magnetic contact with the top slab. The hydraulic actuator then causes the electromagnets to lift the slab. The trolley mechanism then positions the slab over the furnace charging table. The mechanism then lowers and releases the slab onto the furnace charging table.
A programmed control unit reads the slab""s weight, lift and transfer path.
Lifting the slabs (as opposed to pushing them off the stack) minimizes marking and deformation of the slabs, enabling a higher quality end product. The present invention also provides increased production rates by transferring a 1000xc2x0 F. slab in about 36 seconds as compared to the pushing mechanism transfer time of about 45 seconds. Production capacity is increased to 300 slabs in an 8-hour period.